SMC stands for sheet moulding compound and BMC for bulk moulding compound.

SMC and BMC compositions typically contain an unsaturated polyester (UP) resin, a filler, processing aids such as a releasing agent and a thickening agent, glass fibre, and a cure system. The cure system typically comprises a peroxide initiator and sometimes an accelerator. Said compositions usually are stable at ambient temperature in an uncured form for several months, i. e. they have a long shelf life or pot life.

Interior and exterior automotive parts require a high dimensional stability, no or low shrinkage, and high surface gloss. For these reasons, nowadays low profile (LP) and/or low shrink (LS) additives are frequently added to SMC and BMC compositions. However, these additives-which are typically formulated in styrene-are used in considerable amounts and they may interfere with the cure and lead to a high residual (i. e. unreacted) styrene content in the SMC/BMC parts. Moreover, their use may also give rise to an unpleasant smell and to volatile compounds other than styrene.

Hence, SMC/BMC parts prepared from compositions that belong to the prior art have a number of drawbacks including a too high total volatiles content (these volatiles include compounds such as benzene, styrene, acetone, methyl acetate, tert-butylalcohol, 1, 2-propanediol, and 2-ethylhexanol, some of which are formed after the decomposition of certain peroxide (s) used in the cure system), in particular a too high benzene content, and bad smell. For example, tert-butyl peroxybenzoate (e. g. Trigonoxo C, ex Akzo Nobel) is commonly used in cure systems for SMC/BMC parts, but the use of this peroxide causes the formation of high levels of benzene.

WO-A-95/13318 to Ashland discloses the use of a polycapped oligomer in SMC resin compositions for enhancing the performance of thermoplastic low profile (LP) additives which improve the surface quality (i. e. a better class"A"surface) of moulded composites such as automotive body panels. In Example 1 on page 18 of this document, compositions are shown comprising an unsaturated polyester resin, an LP additive, a mixture of two peroxides, i. e. one having a one-hour half-life temperature of 64°C and the other of 86°C, and a cobalt salt accelerator. On page 2, lines 14-15, it is mentioned that the use of a polycapped oligomer appears to eliminate the"smoking, "i. e. an increase in volatiles released when the mould is opened, sometimes seen when moulding SMC.

JP-A-09227611 to Kayaku Akzo discloses peroxide compositions which are useful for curing and moulding unsaturated polyesters (SMC and BMC). Said compositions contain a peroxide having a decomposition temperature of 83- 120°C when its half-life is 10 hours, a peroxide having a decomposition temperature of 40-83°C when its half-life is 10 hours, and a phenolic compound showing polymerisation-inhibiting activity. A composition is disclosed comprising a polystyrene shrinkage-reducing agent, a mixture of two peroxides, i. e. one having a one-hour half-life temperature of 98°C and the other having a one-hour half-life temperature of 117°C, and 2, 6-di-t-butyl-4-methylphenol. It is mentioned that the peroxide composition gives an appropriate curing velocity to SMC and BMC, the SMC and BMC compositions have a long pot life and shelf life, and the fibre reinforced products have an improved surface external appearance.

US 5,380, 799 relates to the room temperature curing of a resin composition comprising a mixture of thermoplastic polymers of vinyl acetate and an epoxy compound, a dialkyl-p-toluidine accelerator, a low temperature free radical peroxide initiator, and an alkali metal or transition metal compound. A preferred initiator is a blend of cumene hydroperoxide and acetyl acetone peroxide, the one-hour half-life temperatures of which are both higher than 100°C.

These documents do not relate to the problems underlying the present invention, i. e. reducing the total volatiles content and the smell of the cured SMC/BMC product. The composition of the present invention-which typically does not contain a dialkyl-p-toluidine accelerator-is not disclosed or suggested in either of these documents.

Hence, there is a need in the art for a composition which does not have the aforementioned drawbacks. The present invention provides a composition which can be used for preparing SMC and BMC automotive parts having a low total volatiles content, in particular a low benzene content, and having low smell. It is desired that the uncured composition has a storage stability of at least 4-6 weeks, preferably 3-6 months at 20°C. In the art, it is further desired that the SMC and BMC parts have a good surface quality, preferably a so-called class A surface. Also, it is preferred in the art that the composition be a fast- curing composition, which reduces the residual styrene content and shortens the production time. Finally, it is preferred that the composition does not need an additional postcure.

The composition of the present invention comprises: (a) an unsaturated polyester resin, (b) a suitable low profile or low shrink additive or a mixture thereof, (c) a mixture of at least two peroxides neither of which contains a benzoyl group, one having a one-hour half-life temperature of 100°C or lower and the other having a one-hour half-life temperature of higher than 100°C, and (d) a transition metal salt or complex.

The unsaturated polyester (UP) resin to be used in accordance with the present invention may be any known resin commonly used for making SMC/BMC parts.

Suitable UP resins include high-reactive ortho-or iso-phthalic acid resins, pure maleic acid resins, and mixtures thereof. Examples of suitable UP resins for use

in accordance with the present invention include Palapreg P18, Palapreg P17, and Synolite 0423.

Low profile (LP) and low shrink (LS) additives are known to a person of ordinary skill in the art. LP additives improve the surface smoothness or"profile"of SMC/BMC parts. LS additives reduce shrinkage during the curing of SMC/BMC parts. Preferably, for use in accordance with the present invention, only those additives are used which result in cured SMC and BMC products having a total volatiles content lower than 100 zig C/g SMC/BMC (a maximum limit set by the automotive industry in accordance with VDA 277), preferably lower than 50, more preferably lower than 25 zu C/g SMC/BMC ; a residual styrene content lower than 0.05%, preferably lower than 0. 01 % ; a benzene content lower than 1 C/g SMC/BMC, preferably lower than 0.6 pg C/g SMC/BMC ; and a smell lower than 3 (in accordance with VDA 270 B2), more preferably lower than 2.5, even more preferably lower than 2. These parameters are defined in the Examples described below and using the description and the Examples of the present invention, one of ordinary skill in the art can easily determine whether or not the additive is suitable for use in accordance with the present invention.

Preferably, said LP or LS additive does not contain benzene. More preferably, in the composition of the present invention use is made of an LP or LS additive which forms a dispersion or a suspension in combination with the UP resin.

Suitable LP and LS additives are based on polystyrene, saturated polyester, polyvinylacetate or polyurethane. Examples of suitable additives include Palapreg H852 (a saturated polyester resin, LP additive, ex DSM-BASF), Palapreg H814 (a polystyrene resin, LS additive, ex DSM-BASF), Palapreg H1080 (a polyvinylacetate, LP additive, ex DSM-BASF), LP40A (a polyvinylacetate, LP additive, ex Union Carbide), and LP 138-46 (a polyurethane, LP additive, ex Ashland).

A typical SMC/BMC composition contains 50-90, preferably 60-80, more preferably 65-75 parts by weight of UP resin and 10-50, preferably 20-40, more preferably 25-35 parts by weight of LP/LS additive, respectively. The amounts of the other constituents of the claimed SMC/BMC composition are expressed in parts by weight per a total of hundred parts by weight of UP resin plus LP/LS additive, abbreviated as"phr." Any mixture of at least two peroxides which fulfills the criterion defined above is suitable for use in accordance with the present invention. In the context of the present invention, the term"one-hour half-life temperature"is abbreviated as HLT. Suitable peroxides having an HLT of 100°C or lower include di (3,5, 5- trimethylhexanoyl) peroxide (e. g. Trigonoxo 36, ex Akzo Nobel), 2, 5-dimethyl- 2,5-di (2-ethylhexanoylperoxy) hexane (e. g. Trigonox° 141, ex Akzo Nobel), 1,1, 3, 3-tetramethylbutyl peroxy-2-ethylhexanoate (e. g. Trigonoxo 421, ex Akzo Nobel), tert-amyl peroxy-2-ethylhexanoate (e. g. Trigonoxo 121, ex Akzo Nobel), and tert-butylperoxy 2-ethylhexanoate (e. g. Trigonox° 21, ex Akzo Nobel).

Suitable peroxides having an HLT higher than 100°C include 1,1-di (tert- butylperoxy)-3, 5, 5-trimethylcyclohexane (e. g. Trigonoxo 29, ex Akzo Nobel), 1, 1-di (tert-butylperoxy) cyclohexane (e. g. Trigonox# 22, ex Akzo Nobel), tert- butyl peroxy-3, 5, 5-trimethylhexanoate (e. g. Trigonoxe 42S, ex Akzo Nobel), tert- butylperoxy isopropyl carbonate (e. g. Trigonox# BPIC, ex Akzo Nobel), tert- butylperoxy 2-ethylhexyl carbonate (e. g. Trigonoxe 117, ex Akzo Nobel), and ter-amyl peroxy 2-ethylhexyl carbonate (e. g. Trigonox# 131, ex Akzo Nobel).

Preferably, in accordance with the present invention, a mixture of two peroxides is used, one having an HLT of 75-95°C, more preferably 85-95°C, and the other having an HLT of 105-125°C, more preferably 110-120°C.

Particularly useful mixtures of peroxides to be used in accordance with the present invention include Trigonox° 21 (HLT of 91°C) and Trigonoxe 117 (HLT of 117°C), Trigonoxo 121 (HLT of 91°C) and Trigonoxo 117, Trigonox"141

(HLT of 86°C) and Trigonox 131 (HLT of 113°C), and Trigonoxo 21 and Trigonoxo BPIC (HLT of 117°C).

The total amount of peroxide to be used in accordance with the present invention typically is in the range of 0.5-2. 5, preferably 1-2, more preferably 1.4- 1. 6 phr.

In accordance with the present invention, a transition metal salt or complex is used as an accelerator for the cure. Suitable transition metal salts and complexes are known to a person skilled in the art. Mixtures of transition metal salts, transition metal complexes or of a transition metal salt and a transition metal complex may also be used in the composition of the present invention.

Examples of suitable transition metal salts and complexes include manganese naphthenate, cobalt naphthenate, cobalt octanoate, copper naphthenate, copper acetate, and cobalt acetate.

Preferably, a cobalt (Co) salt or complex, a copper (Cu) salt or complex, or a mixture thereof is used in accordance with the present invention. Any cobalt and/or copper salt or complex may be used in the composition of the invention.

Suitable accelerators include cobalt salts (e. g. Accelerator 6050, ex Akzo Nobel), such as cobalt octanoate (e. g. Accelerator NL-51 P, ex Akzo Nobel), and cobalt complexes (e. g. Accelerator 383, ex Akzo Nobel). Preferably, a mixture of a cobalt salt or complex and a copper salt or complex is used in accordance with the present invention. A particularly suitable accelerator is a complex containing cobalt acetate and copper acetate, which is available as Accelerator R-553 from Akzo Nobel.

The amount of accelerator to be used in accordance with the present invention typically is in the range of 0.1-2, preferably 0.2-1, more preferably 0.4-0. 6 phr.

Typically, the composition of the present invention further contains a filler such as calcium carbonate or calcium sulfate, a releasing agent such as zinc stearate

or calcium stearate, a thickening agent such as magnesium oxide, magnesium hydroxide, calcium oxide or calcium hydroxide, and glass fibre reinforcement.

These components are added to the composition of the invention in their conventional amounts. The SMC/BMC composition may optionally also contain other conventional additives including wetting and dispersing additives, pigments, inhibitors, promotors, and stabilizers.

A typical SMC/BMC composition comprises 50-90 parts by weight of UP resin, 50-10 parts by weight of LP/LS additive (a total of 100 parts by weight of resin plus additive), 100-300 phr of a filler, 0.1-10 phr of a releasing agent, 0.1-5 phr of a thickening agent, 50-150 phr of glass fibre, 0.5-2. 5 phr of a mixture of at least two peroxides, and 0.1-2 phr of an accelerator. A preferred SMC/BMC composition comprises 60-80 parts by weight of UP resin, 20-40 parts by weight of LP/LS additive (a total of 100 parts by weight of resin plus additive), 150-250 phr of a filler, 3-7 phr of a releasing agent, 0.5-3 phr of a thickening agent, 70- 100 phr of glass fibre, 1-2 phr of a mixture of two peroxides, and 0.2-1 phr of an accelerator.

The composition of the present invention typically is cured sunder pressure in a hot mould in a conventional way using known methods and equipment. The cure temperature typically is in the range of 100-200°C, preferably 130-170°C, more preferably 140-160°C. The cure time typically is from 0.1-60 min, preferably 0.5-10 min, more preferably 1-5 min.

The present invention is illustrated by the following Examples.

EXAMPLES The residual styrene content (expressed in m/m%) was determined in accordance with GC/94.5. The technique used is capillary gas chromatography with split injection and flame ionization detection. The sampel is extracted with dichloromethane, and the extract is separated in a chemically bonded non-polar

stationary phase. The styrene content is determined according to the internal standard method using tert-butylbenzene as the internal standard.

The smell was determined in accordance with VDA 270 B2. In this method, part of the SMC/BMC product is put in a glass pot above a certain amount of water.

This glass pot is put into an oven at 40°C during 24 hrs. After this time, a panel of 5 people judges the smell of these samples on a scale of 1 to 6, where 1 means the smell is not noticeable and 6 means the smell is intolerable.

The total volatiles content (expressed in llg C/g SMC/BMC product) was determined in accordance with VDA 277 (a VW/Audi automotive industry standard). The technique used is static headspace capillary gas chromatography with split injection. A fixed weight of sample particles is transferred to a 20 mi septum vial. The septum vial is placed in the oven (at 120°C) of the headspace sampler. After 5 hrs, 1 ml of the headspace gas is transferred to the GC and is separated in a chemically bonded non-polar stationary phase. The lig C/g content of emitted volatile components is determined according to the external standard method using acetone as the external standard. The method is a relative method and allows one to compare different samples.

The benzene content was calculated from the total volatiles content and is also expressed in p. g C/g SMC/BMC product.

Examples 1-8 and Comparative Examples A-D (BMC products) UP-resin: Palapreg P17, LP additive Palapreg H852 or LS additive Palapreg H814 or LP additive LP138-46, weight ratio resin/additive of 70/30, Cure temperature: 150°C, Cure time: MMT plus 60 sec (MMT=Minimum Moulding Time, expressed in sec). The type and the amount of cure system (Tx= Trigonox@, Acc. =Accelerator) are indicated in Table 1 and expressed in phr.

Each composition consisted of (in phr): UP resin, 70; LP/LS additive, 30; Durcal 5,200 (a filler) ; zinc stearate, 5 (a releasing agent); Luvatol MK35,1. 5 (a thickening agent); glass, 75; peroxide mixture, 1.5 ; and accelerator, 0.5.

Except for the filler and the glass, the components were mixed to homogeneity.

This mixture was poured into a Z-blade mixer (Heligear Z-blade mixer type HDMO, capacity 1 kg or IKA-Duplex-kneter HKD10, capacity 4 kg). The filler was dosed to this mixture within 1 min and mixed for 1 min, then the glass was dosed within 2 min and mixed for 3 min, giving a homogeneous compound (BMC). The compound was thickened for a period of time of at least 4 days.

This compound was cured in a reactometer (Reactometer SMC Technology, ex Derek & Roger OHG) under the conditions described above. An amount of 240 g of the compound was put into a mould of 12x25 cm. The mould was closed and put under a pressure of 100 bar-i. e. 100x105 Pa- (trigger pressure of 65 bar) during the cure time (MMT plus 60 sec). Then, the mould opened automatically and the pressed plate (thickness approx. 4 mm) was taken from the mould and the sample was analyzed as described above.

Examples 2 to 8 show that independent of the cure system and additive used, results were obtained which fulfill the requirements of the automotive industry with respect to total volatiles content, in particular benzene content, and smell.

The MMT and the efficiency (evident from the residual styrene content) of the exemplified compositions are also satisfactory. The shelf life of all tested compounds was more than 3 months.

Examples 9-11 (SMC products) UP-resin: Palapreg P18, LP additive Palapreg H852 or LS additive Palapreg H814, weight ratio resin/additive of 70/30. The type and the amount of cure system (Tx= Trigonox@, Acc. =Accelerator) are indicated in Table 2 and expressed in phr.

Each composition consisted of (in phr): UP-resin, 70; LP/LS additive, 30; BYK W9010,1. 5 (a wetting and dispersing additive); Millicarb OG, 200 (a filler) ; zinc stearate, 4.5 (a releasing agent); and Luvatol MK35NV, 1.9 (a thickening agent). The glass added is expressed as glass weight and was 28 m/m% of the total compound.

The base viscosities were determined with Brookfield viscometers RVT and HBT, spindle 6,10 rpm at 30°C. The thickening of all compositions was measured with a Brookfield HBT at room temperature. Each composition was prepared in an amount of 9-10 kg in the form of an SMC paste, as follows : 1. The resin, LP/LS additive, wetting and dispersing additive, releasing agent, and cure system were weighed in a mixing tank and were mixed at a low speed (a circumferential speed of 6.4 m/s) under a dissolver.

2. The filler was weighed and dosed at low mixing speed (a circumferential speed of 6.4 m/s) to the resin-containing mixture.

3. The dispersion was mixed during 2 min at high speed (a circumferential speed of 15.6 m/s).

4. The thickening agent was weighed and then added while mixing at a low speed (a circumferential speed of 6.4 m/s) during 1 min.

Directly after the final mixing step, the SMC pastes were dosed to the doctor blade boxes of a Schmidt & Heinzmann SMC laboratory line (HM-LB-23) to produce SMC products with a weight of around 4,000 200 g/m2 and a glass content of 28 3%.

After a period of 3-8 days for thickening, the SMC products were moulded on a 160 ton Zeulenroda press in a 30x40 cm steel mould to produce plates with a thickness of 2.5-3. 5 mm. The pressure on the plate during the moulding was between 80 and 100 bar. The moulding time was varied between 90 and 180 seconds at moulding temperatures of 145-155°C. The results of Examples 9-11 for SMC products are comparable to the results obtained for the BMC products of Examples 2-8 and the same conclusions can be drawn.

Table 1. Results of BMC products Example Cure quantity LP or LS additive Residual Smell Total Benzene MMT System styrene Volatiles (phr) (m/m%) (VDA 270 B2) (µg C/g) (µg C/g) (sec) A TxC 1.5 Palapreg H852 0.17 3.0 158 5.6 59 B Tx117/Tx21 1.25/0.25 Palapreg H852 0.01 2.0 148 0.8 34 C Tx21/Tx141 1.25/0.25 Palapreg H852 0.35 2.8 303 0.1 20 Acc.R-533 0.5 D Tx117/Tx29 1.25/0.25 Palapreg H852 <0.01 2.2 113 0.4 45 Acc.R-553 0.5 1 Tx117/Tx21 1.25/0.25 Palapreg H852 <0.01 1.8 54 0.4 34 Acc.R-553 0.5 2 Tx117/Tx121 1.25/0.25 Palapreg H852 0.02 2.2 73 0.4 34 Acc.R-553 0.5 3 Tx117/Tx21 1.25/0.25 Palapreg H814 0.02 2.4 78 ND* 28 Acc.6050 0.5 4 Tx131/Tx141 1.25/0.25 Palapreg H814 0.04 2.0 89 0.3 28 Acc.6050 0.5 5 TxBPIC/Tx21 1.25/0.25 Palapreg H814 <0.01 2.4 88 ND* 27 Acc.6050 0.5 6 Tx117/Tx121 1.25/0.25 Palapreg H814 <0.01 2.6 70 0.6 26 ACc.383 0.25 7 Tx117/Tx121 1.25/0.25 Palapreg H814 0.03 2.0 72 0.5 28 Acc.R-553 0.5 8 Tx117/Tx21 1.25/0.25 LP 138-46 <0.01 2.4 99 0.3 25 Acc.6050 0.25 *ND=Not Detected Table 2. Results of SMC products Example Cure Quantity LP or LS Residual Smell Total Benzene system additive styrene Volatiles (phr) (m/m%) (VDA 270 B2) (µg C/g) (µg C/g) 9 Tx117/Tx21 1.25/0.25 Palapreg H852 0.01 2.0 90 0.3 Acc.R-553 0.5 10 Tx131/Tx141 1.25/0.25 Palapreg H852 <0.01 2.8 45 0.1 Acc.R-553 0.5 11 Tx117/Tx21 1.25/0.25 Palapreg H814 0.04 2.4 63 0.1 Acc.R-553 0.5